Based on the advantage of infrared spectroscopy which can quickly measure the oil oxidation area,a new method of using infrared oxidation area to describe the lubricating oil acid value was put forward through the relevance analysis of IR oxide area and oil acid value which was measured by routine method.The new prepared aviation lubricating oil samples and the used oil samples were analyzed by this method.The infrared spectra from 1 800 to 1 670 cm-1 was selected as the oxidation zone for determining their acid value,and the correlation of the acid value and the peak area of infrared spectrum of the standard oil samples and used oil samples was analyzed respectively.The regression equations were proposed and corrected.The results show that the method to determine the acid value of new and used lubricating oils by FTIR is feasible and reliable.